<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .a {
        color: red;
      }
      .b {
        font-size: 40px;
      }
      .c {
        background: yellow;
      }
    </style>
  </head>
  <body>
    <div class="a b" id="box">hello box</div>
    <script>
      const box = document.getElementById("box");
      box.classList.add("c", "d", "e");
      box.classList.remove("c", "a", "b");
      console.log(box.classList.contains("e"));
      console.log(box.className);
    </script>
  </body>
</html>
